Tim,
What algorithm does the HP50G use to find the roots of polynomials? Is it the JenkinsTraub algorithm? The HP50G seem to have a polynomial roots solver that works pretty well.
Namir
Question for Tim Wessman


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08312010, 02:15 PM
Tim, What algorithm does the HP50G use to find the roots of polynomials? Is it the JenkinsTraub algorithm? The HP50G seem to have a polynomial roots solver that works pretty well. Namir ▼
08312010, 04:04 PM
I assume you are talking about the PROOT command, or the Solve Poly interface? This is what is found in the source there:
** The algorithm is Laguerre iteration with stepsize control
** The implementation is a modified version of the HP71 Math TW
Edited: 31 Aug 2010, 4:06 p.m. ▼
08312010, 05:19 PM
More information about the HP71B Math ROM Polynomial Root Finder can be found in the July 1984 issue of HewlettPackard Journal, pages 33 through 36:
08312010, 08:50 PM
Thanks Tim ... gives me a good insight of how the 50G (and other graphing machines) handle getting the roots of polynomials. Namir
08312010, 09:35 PM
Tim and Gerson, I was looking at the HP71B Math Pac manual and it does mention the Laguerre method as being used for that ROM (and I am sure for many other HP calculators). I have a Matlab function that implements of the Laguerre method and it works very well ... so the method is good, even though my implementation is bare bone  not scaling or other programming tricks.
Namir Edited: 31 Aug 2010, 10:33 p.m. ▼
09032010, 03:04 AM
Hi Namir, You may be interested by the discussion/comparison of several Polynomial Rootfinder programs as well as the matlab sample program (Appendix A) in this document: Iterative Methods for Roots of Polynomials
Regarding PROOT on HP calculators, the following post from Bill Wickes on comp.sys.hp48 back in 1992 shows that it was quite easy to port HP 71B assembler functions to the HP48:
Given this, I'm a bit surprised that the results for the second test on the HP 71B (+ Math Pac) and the HP 48GX (same CPU, same algorithm, same assembler code?) or the 49G+ in the following post on this forum are somewhat different (The Turtle (HP71B) and the Hare (HP49G+) [LONG]): 0.999999999944, 1.312E12 for the HP 71B ... the HP 71B while being the oldest machine is the closest to the exact result (1,0)!
Edited: 5 Sept 2010, 6:03 a.m. 
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